1. Field of the Invention
The present invention relates to a method of manufacturing a toner, a toner, a two-component developer, a developing device and image forming apparatus.
2. Description of the Related Art
In a traditional method of kneading and pulverizing, the shape and surface composition of a toner are difficult to purposefully control up to desired extents. The toner indefinite in shape cannot have sufficient fluidity even by adding thereto a fluidizing agent, and besides, such a toner has problems that the fluidizing agent deposited on the toner surface comes to be buried in hollows on the toner surface, thereby causing fluidity degradation over time, and there occur deteriorations in developability, transferability, cleaning properties and so on. As to the transferability in particular, the toner indefinite in shape has an increased adhesion force because of, e.g., an increase in number of contact points, so it tends to suffer more marked deterioration in transferability. A further increase in amount of fluidizing agent added with the intention of solving those problems causes other problems that black spots develop on a photoreceptor and, in the case of a two-component developer, adhesion of the fluidizing agent to the carrier occurs to result in the lowering of chargeability.
Such being the case, an emulsion aggregation method is proposed as a toner manufacturing method substituting for the method of kneading and pulverizing. The toner manufactured by emulsion aggregation is superior in sharpness of particle size distribution and uniformity of toner shapes, and besides, features on its manufacturing method allow extensive control of toner shapes, from spherical to irregular shapes. Therefore, excellent chargeability, transferability and cleaning properties can be attained.
In the emulsion aggregation method, a toner is generally manufactured by preparing fine dispersions of individual toner ingredients, such as a binder resin, a colorant and a release agent, mixing the dispersions to form aggregated particles of a desired toner size, and then fusing and uniting together the ingredients under heating. Although the formation of aggregated particles is generally carried out in the presence of a flocculant, the desired composition is difficult to ensure to the particles formed because the aggregates formed by addition of a flocculant are relatively weak in cohesion force and easily liberate toner ingredients including a coloring agent.
Methods hitherto proposed as solutions to such a problem aim at preventing liberation of toner ingredients by forming aggregated particles through heteroaggregation. However, since aggregation in such methods does not progress evenly in the interior of particles and uneven aggregation occurs among colorant particles, the method fails to provide a toner of a satisfactory coloring power.
According to related art disclosed in Japanese Unexamined Patent Publication JP-A 2001-228647, a fine-particle resin dispersion in which fine particles of resin 1 μm or below in size are dispersed, a colorant dispersion, a release agent dispersion and an inorganic fine-particle dispersion are mixed together and subjected to heteroaggregation, thereby preparing an aggregated particle dispersion, and then the ingredients in each aggregated particle are fused and united together by heating to a temperature higher than the glass transition temperature of the fine-particle resin. Thus, this art allows providing a toner for electrostatic charge development, which ensures high surface gloss of fixed images, high transparency in the case of output to OHP (Overhead Projector) sheet and excellent fixation characteristics including bending resistance of fixed images, and forming images of excellent quality.
According to related art disclosed in Japanese Unexamined Patent Publication JP-A 2004-20585, sulfonium group-containing cationic particles and anionic particles prepared by an in-liquid drying method are made to undergo heteroaggregation in an aqueous medium, thereby controlling presence positions of pigment (colorant) and wax in a toner so that the colorant in the toner is present more densely as its position nears the toner core, while the wax in the toner is present more densely as its position nears the toner surface. Thus, this art makes it possible to provide a toner having high charging stability under high humidity, excellent long-term running properties and a wide non-offset range.
In the related art disclosed in JP-A 2001-228647, however, the dispersibility of a colorant becomes low due to uneven aggregation, so the toner having high transparency and coloring power cannot be obtained.
In the related art disclosed in JP-A 2004-20585, on the other hand, the colorant distribution in a toner is not uniform, so the toner obtained cannot have high transparency and coloring power.